The goal of this project is to define the molecular mechanisms involved in the replication of enveloped RNA viruses and, in particular, to understand the factors which influence the regulation and expression of viral genetic information. The possible role of the viral RNA genome in directing virus assembly as well as certain aspects of viral RNA metabolism are being investigated in a system which uncouples murine leukemia virus RNA synthesis from terminal steps in virus maturation. Results of a recent kinetic study indicate that viral messages have a very slow rate of turnover, whereas viral RNA which is ultimately encapsidated into virions has a short half-life. This finding suggests that genome-size viral RNA is present in two independent metabolic pools in the infected cell. Another interest concerns the process of reverse transcription, and in this connection recombinant DNA technology is being used to map the genetic lesion in a nonconditional reverse transcriptase mutant. Work has also been carried out on chromosome-mediated transfer of viral genetic information.